ASVAB Mechanical Comprehension Practice Test 579691 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.21
Score	0%	64%

Review

1 If 45 lbs. of force is applied 6 ft. from the fulcrum at the blue arrow and the green box is 5 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

62% Answer Correctly

	0 lbs.
	54 lbs.
	108 lbs.
	27 lbs.

Solution

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{45 lbs. \times 6 ft.}{5 ft.} \) = \( \frac{270 ft⋅lb}{5 ft.} \) = 54 lbs.

2 If the radius of the axle is 7 and the radius of the wheel is 10, what is the mechanical advantage of this wheel and axle configuration?

36% Answer Correctly

	1
	0
	10
	-3

Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

3 If input effort is 200 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 4?

79% Answer Correctly

	400ft⋅lb
	0ft⋅lb
	800 ft⋅lb
	50ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 4 will multiply an input effort of 200 ft⋅lb by 4 to produce an output effort of 800 ft⋅lb.

Which of the following surfaces would have the lowest coefficient of friction?

85% Answer Correctly

	leather
	concrete
	tile
	ice

Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

5 If the force applied at the blue arrow over 2 ft. moves the green box 0.25 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	1
	8
	24
	16

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{2 ft.}{0.25 ft.} \) = 8

You might be wondering how having an effort distance of 8 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 8 times the resistance distance, the effort force must be \( \frac{1}{8} \) the resistance force. You're trading moving 8 times the distance for only having to use \( \frac{1}{8} \) the force.